1. Field of the Invention
The present invention relates to a manufacturing method for a metal bonded grinding tool and the metal bonded grinding tool produced thereby.
2. Description of the Prior Art
As a prior art method for manufacturing a metal bonded grinding wheel, the manufacturing method disclosed in U.S. Pat. No. 3,588,992 to Asaeda et al is known, which method includes the steps of:
A. A PRELIMINARY PRETREATING STEP IN WHICH ABRASIVE GRAINS HAVE THEIR SURFACES CLEANED AND PREPARED FOR SUBSEQUENT METAL COATING;
B. A PRESS-FORMING STEP IN WHICH THE ABRASIVE GRAINS PRETREATED IN (A) ARE PRESS-FORMED TO SPECIFIED STRUCTURAL DIMENSION;
C. A BOND METAL COATING STEP IN WHICH THE PRESS-FORMED ABRASIVE GRAINS OBTAINED IN STEP (B) ARE PLACED IN A SOLUTION CONTAINING A METALLIC SALT AND THE SOLUTION IS FORCIBLY PASSED THROUGH THE SPACES BETWEEN THE ABRASIVE GRAINS, WHEREBY MAKING THE METAL PRECIPITATE ON THE SURFACES OF THE ABRASIVE GRAINS AND BINDING THESE ABRASIVE GRAINS WITH THE PRECIPITATED METAL; AND
D. A HEAT TREATMENT STEP FOR CRYSTALLIZING THE PRECIPITATED METAL.
Generally, the grinding wheel made by the foregoing steps has a thickness T larger than the width W as shown in FIG. 1, EQU width: W &lt; Thickness; T (1)
and in the foregoing step (c), as shown in FIG. 3, a press-formed body, that is, the grinding wheel portion 3 of the abrasive grains provided around a rim 2 which holds a centering metal 8 at the center thereof is provided in a frame 1 coaxially thereto, and the frame 1 is sealingly held by an upper body 4 and a lower body 5. Solution is introduced through a conduit 6 connected to the lower body 5 and is forcibly passed through the spaces between the press-formed abrasive grains in an axial direction of the grinding wheel portion 3. That is, the solution moves in a direction shown by the arrow marks, and is finally exhausted from an outlet conduit 7 which is provided on the upper body 4, whereby the metal is precipitated on the surfaces of the abrasive grains. In the prior art grinding wheel, the rim 2 is made of a usual solid metal such that the solution can be passed in the axial direction of the grinding wheel only through the spaces among the abrasive grains. However, uniformity of the bonding metal can be obtained by the foregoing solution supply method while the relationship shown in the above formula 1 holds good, because the solution passage area is relatively wide. On the contrary, in the case that it is required to bond a diamond grinding wheel, shown in FIG. 3, which grinding wheel has the following dimensional relationship:
Grinding wheel width: EQU W &gt; Grinding wheel thickness: T (2)
it is inadequate to adopt the above noted prior solution supply method, in which the solution is passed through the grinding wheel portion 3 in an axial direction of the grinding wheel, because the precipitated bonding layer is apt to become uneven in the axial direction of the grinding wheel. This is because the solution can only pass through the grinding wheel portion which is thin in thickness (T) and wide in width (W) in the axial direction thereof. In addition, it is desired that the grinding wheel portion 3 is strongly affixed to the rim 2 in accordance with the development of heavy and high speed grinding by the diamond grinding wheels. However, in accordance with the foregoing prior technique, there is a further defect that it is unavoidable to generate a boundary portion between the rim 2 and the grinding wheel portion 3, and thus, the bonding force therebetween becomes weak.